Ignition of fuel for lighting a well



on. BEARING STRATUM INVENTOR LEONARD W. EMERY June 21, 1960 L. w. EMERY IGNITION OF FUEL FOR LIGHTING A WELL Filed Sept. 26, 1956 PRIMARY o CONTAINING e SECONDARY GAS United States Patent 2,941,595 7 IGNITION F FUEL FOR LIGHTING A WELL Leonard W. Emery, Humboldt, Kaus assignor to Sinclair g}! 8: Gas Company, Tulsa, Okla., a corporation of aine Filed Sept. 26, 19-56, Ser. No. 612,142

10' Claims. or. 166- 38) This invention relates to the heating of underground formations, and, more particularly, the invention is concerned with a method for heating or lighting a subterranean stratum opposite a well bore through production of a spontaneously ignitable material in the bore with subsequent mixing of this material, a free oxygen-containing gas and a hydrocarbon fuel at a desired position in the bore to provide combustion.

It has been proposed to heat underground formations for various purposes usually associated with increasing recovery of oil by secondary recovery methods. For instance, heat may be applied in the immediate vicinity of a well bore to lower the viscosity of surrounding hydrocarbon materials. A more important use of the heating lies in connection with in-situ combustion procedures. In a particularly advantageous method of this type, a fuel such as methane is combusted in an input well bore to heat the first few feet of adjacent petroliferous stratum to a temperature generally greater than about 400 F., e.g. about 600 to 1200" F., to establish combustion in the stratum. This procedure is often referred to as well lighting. In one recovery method a cooling gas which will not support combustion can then be injected and as a result the heat front is moved into the formation away from the input well bore. A free oxygen-containing gas is subsequently injected to move the combustion front towards one or more output wells. By this method the hydrocarbon content of the formation is moved towards the output well, and substantially all of the oil can be swept from the formation traversed by the combustion or heat wave.

Usually in Well heating or lighting procedures a burner device is lowered into the well to the vicinity of a bare formation which is to be heated or lighted. Aside from having to provide an apparatus which satisfactorily mixes and burns air and fuel in the Well for starting combustion in the stratum, considerable difiiculty has been experienced in providing conditions conducive to the initial heating of the fuel and oxygen-containing .gas' to combusting temperatures.- Sometimes a sparking device is employed as a means for igniting a hydrocarbon fuel-air stream. Difiiculties arise in these devices due to complications in the burner structure and the fact that the operator is several hundred feet from the level of burning. Depending upon the location and depth of the well, elevated pressures and temperatures may be encountered which affect the operation of the burner. Also electrical conductors must be employed and this gives rise to problems concerned with stringing the conductors and proper construction as to wire sizes and electrical and thermal insulation. Needless to say, these various factors can be responsible for excessive costs and difficulties in. operation, particularly as the operator increases the distance the burner is projected into the Well bore.

In the method of the present invention for heating or lighting a subterranean stratum many of the disadvantages of prior methods are avoided. In my method I generate a spontaneously combustible reaction prodnot in a well bore through contact of water and a chemical material or substance reactive with the water, which material is disposed in the well in a more or less sta tionary manner in the vicinity of the stratum to be heated. The reaction product is mixed with a free oxygen-containing gas and a hydrocarbon fuel to provide combustion at the desired location in the well bore.

in this method the reactive material, eg a solid metal phosphide, can be placed in a perforated or other open container and then lowered on a wire line to the desired location in the well. Water is then injected into the well to contact the reactive material for generation of the spontaneously ignitable product which mixes withor contacts oxygen supplied to provide combustion. This initial combustion then ignites in the oxygen a gaseous or liquid hydrocarbon fuel made available. After combustion of the hydrocarbon fuel is established, water injection can be stopped and the perforated container withdrawn from the Well through a lubricator arrangement at the well head. Combustion of the hydrocarbon fuel can be continued until the adjacent stratum is sufficiently heated. A particular advantage of my method lies in its ability to be used under diverse well conditions, for instance temperatures of about 50 to 350 F.-or more and pressures from about atmospheric to 10,000 lbs. or

more.

Perhaps the method of the present invention can be best described by reference to a particular operating pro cedure as illustrated in the drawing which is a diagrammatical sketch of a well bore equipped with a useful tubing arrangement and a perforated container in the bore holding the material which is reactive with water to produce the spontaneously ignitable reaction product.

The well is 4,210 feet deep to the top of the oil sand and a well head pressure of 1750 p.s.i.g. will force gas freely into the oil sand. A 4" steel tubing 1 is cemented at 2 in a 6 bore, and the tubing extends down the oil sand. Below the lower end of the tubing is a bare hole several feet in height. Inside of tubing 1 is placed a 1" diameter steel tubing string 3 which reaches from the oil sand through the well head 4 extending across tubing 1. Primary air at 1750 p.s.i.g. pressure and at the rate of 1000 cubic feet per hour (S'lP) enters'the well through valved 1" diameter steel pipe 5 which goes into tubing 3 just above the well head 4. Gas which is essentially methane is supplied at 1750 p.s.'i.g. pressure and at the rate of cubic feet per hour (STP) through a valved /2" steel line 6 entering tubing 1 just below the Well head 4. Line 6 continues down the well in the annulus between tubing strings I and 3 and enters tubing 3 a short distance, for instance 5 feet, from its lower end. When using natural gas as the fuel it is preferred that the mixture of air and fuel in the primary combustion tube contain about 5 to 15% by volume of the fuel.

Entering through a stuffing gland-lubricator arrangement (not shown) on the top of tubing 3 is steel wire line 13 which has at its lower end perforated container 14; This container is 36" in height and has an outside diameter of 0.750. The top of container 14 is positioned just below the entry of tubing 6 into tubing 3. In the container are 1000 grams of solid particulate commercial calcium phosphide (Baker and Adamson) which contains some calcium pyrophosphate. The container has screened perforations to avoid loss of the finely divided calcium phosphide through the perforations which are A5 in diameter to allow for water entry and escape of the reaction product. Entering line 5 is a valved /2" steel line 9 through which /2 gallon of Water at the rate of 7 gallons per minute is injected into the primary air. Secondary air under a pressure of 1750 p.s.i.g. and at a rate of 4000 cubic feet per hour (STP) is passed into valved 2" steel line 10 entering tubing 1 below the well head 4,

Thermowell' 11 is located at the lower end of tubing 3 to follow the temperatures during the lighting procedure and it houses a thermocouple (not shown). The leads from the thermocouple pass through thermowell 11 tothe surface at '12.

In operation the secondary air and hydrocarbon fuel flows are started in lines 10 and 6, respectively, and then primary air and water are admitted to tubing 3 through lines and 9. The water enters container 14 and reacts with the calcium phosphide to produce monoand diphosphine which exit the container. The phosphine mixes with primary air and ignites to provide combustion ,of the hydrocarbon fuel. Perforated container 14 can be left in place to provide for a re-light if necessary, but preferably it is withdrawn from the well by taking up on line 13 after combustion of the hydrocarbon fuel is established. To prevent loss of pressure when withdrawing line 13 and container 14, a stuffing box-lubricator arrangement canbe provided on top of tubing 3. If desired, the lower ends of tubings 1', 3 and 6,'the wire line 13 and the container 14 can be made of stainless steel or other heat resisting metals. Also, in practicing this method tubing arrangements for carrying the oxygenconta ining gas, water and hydrocarbon fuel to the vicinity of container 14 other than that shown in the drawing can be employed. For example, the Water could be introduced with the hydrocarbon fuel.

The heating of the stratum can be continued as long as desired, and the character of the combustion and the temperature of the surrounding formation can be followed as by analysis of combustion gases taken from an adjacent output well (not shown). In well lighting procedures the heatingwill usually be continued until the temperature of the adjacent stratum is in the range of 400 to 1200 F. for at least a 2-foot radius around the well bore so that upon supplying a free oxygen-containing gas a combustion wave will be maintained in the formation. The operator may choose to provide extraneous fuel while propagating the heat wave and the combustion wave in the formation.

Generally, the amount of gaseous or liquid hydrocarbon fuel supplied to the well bore will be such that its mixture with all of the oxygen-containing gas available will have a heat of combust on of less than about 40 B.t.u.s per cubic foot. Accordingly, when employing air and a hydrocarbon gas of 1000 B.t.u. per cubic foot quality, the latter is preferably not greater than about 4 volume percent of the total air provided. With lower B.t.u. hydrocarbon fuels increased volumes of fuel can be used to maintain a heat of combustion of about .15 to 40 B.t.u. per cubic foot of total fuel and air mixture. The quantity, if any, of secondary gas supplied will depend upon the desired temperature of the final gas mixture. Whether the secondary gas be inert, air or hydrocarbon fuel it serves primarily to reduce the temperature of the combustion products, for instance, to avoid formation spalling and destruction of metal. It may be desirable to heat the well with a rich fuel-air mixture, i.e, one in which the amount of oxygen is insufficient to burn all of the hydrocarbon fuel. This will avoid obtaining from the output well recycle gases containing free oxygen which might give rise to explosions. Combustion in this case should be essentially complete in the primary burner which would be the case where I supply, for instance, 1000 cubic feet per hour of primary air, 80 cubic feet per hour of 1000 B.t.u. fuel gas and 4000 cubic feet per hour of hydrocarbon or inert secondary gas to provide a mixture of combustion products and secondary gas having a temperature below 1000 F. Should it be desired to heat the stratum through a liner then the fuel-rich gas total mixture with substantially no free oxygen could maintain mix temperatures suitable for liner use without incurring the possibility of obtaining deleteriously high temperatures due torthe presence of carbon andfree oxygen.

Although the method of the present invention has been described mainly with reference to the use of calcium phosphide, other materials which react with water to give a spontaneously ignitable product can be employed. A number of such materials are known, e.g. sodium, potassium and the metal phosphides, particularly those of metals having atomic numbers up to about 40. The various useful phosphides include those of the metals of group I, such as sodium and lithium phosphides, and the group II metal phosphides, for instance those of beryllium and magnesium. Aside from the alkali metal phosphides of groups I and II, among the other metal phosphides which can be employed are those of aluminum and arsenic. These latter phosphides react moderately fast with water to provide a phosphine-containing product but if desired the speed of these reactions can beenhanced by the use of ignition promoters such as nitric oxide. Such promoters also can be employed with the alkali metal phosphides; however, they will usually not be required. I prefer that the reactive material be in the solid state in the well bore.

In the description of my method I have employed the term phosphine to designate both monophosphine and diphosphine. As previously noted the mixture obtained through the reaction of calcium phosphide and water contains both monoand diphosphine, and it is believed that the latter is particularly effective towards making the mixture spontaneously ignitable in a free oxygencontaining gas at moderate temperatures, say 50 to 100 R, which exist in a great many well bores. Mono phosphine is also spontaneously ignitable in a free oxygencontaining gas, but if diphosphine be not present, well bore temperatures of at least about 150 F. are advantageous. I prefer, therefore, to generate in the well bore diphosphine or mixtures of monoand diphosphine, and when such mixtures are provided the diphosphine can ignite at a low temperature to promote the combustion of the monophosphine.

It is claimed:

1. In a method for lighting and continuing combustion of a hydrocarbon fuel in a well bore penetrating a subterranean formation, the steps comprising placing in a stationary position in the bore in the vicinity of a desired location of lighting a fuel, a metal phosphide capable of reacting with water to produce spontaneously combustible phosphine, introducing into said bore a hydrocarbon fuel, an oxygen-containing gas and water to contact the disposed metal phosphide to produce the spontaneously combustible phosphine, and contacting the produced phosphine with said oxygen-containing gas in an amount sufficient to provide continuing combustion of the phosphine and continuing combustion of the fuel by the combustion of the phosphine.

2. The method of claim 1 in which the contacting of the water and the phosphide produces a mixture of monoand diphosphine.

3. In a method for lighting and continuing combustion of a hydrocarbon fuel in a well bore penetrating a subterranean formation, the steps comprising placing in a stationary position in the lower end of a tubing in the Well bore in the vicinity of a desired location of lighting a fuel, a metal phosphide capable of reacting with water to produce a spontaneously combustible phosphine,introducing hydrocarbon fuel through a second tubing in the well bore which enters the first tubing near its lower end, introducing into the well bore through said first tubing an oxygen-containing gas containing water, introducing a secondary gas in the well bore around said first tubing, said water reacting with the metal phosphide to 4. The method of claim 3 in which the contacting of the water and the phosphide produces a mixture of monoand diphosphine.

5. The method of claim 1 wherein the metal of the metal phosphide has an atomic number up to about 4-0.

6. The method of Claim 5 wherein the contacting of water and the phosphide produces a mixture of mono and di phosphine.

7. The method of claim 6 wherein the metal phosphide is calcium phosphide.

8. The method of claim 3 wherein the metal of the metal phosphide has an atomic number up to about 40.

9. The method of claim 8 wherein the contacting of the water and the phosphide produces a mixture of mono and di phosphine.

10. The method of claim 9 wherein the metal phosphide is calcium phosphide.

References Cited in the file of this patent UNITED STATES PATENTS 797,529 Oliph-ant et a1 Aug. 15, 1905 1,806,499 Ranney et a1. May 19, 1931 1,870,320 Adams et a1. Aug. 9, 1932 10 2,747,672 Simm May 29, 1956 OTHER REFERENCES Jones: Inorganic Chemistry, published 1947 by Blak- 15 iston, pages 377 and 378. 

